1. Field of the Invention
Implementations of various techniques described herein generally relate to correcting seismograms for various distortions.
2. Description of the Related Art
The following descriptions and examples do not constitute an admission as prior art by virtue of their inclusion within this section.
In a typical seismic survey, a plurality of seismic sources, such as explosives, vibrators, airguns or the like, may be sequentially activated at or near the surface of the earth to generate energy which may propagate into and through the earth. The seismic waves may be reflected back by geological formations within the earth. The resultant seismic wavefield may be sampled by a plurality of seismic sensors, such as geophones, hydrophones and the like, that may be various distances or offsets from the source. Each sensor may be configured to acquire seismic data at the sensor's location, normally in the form of a seismogram representing the value of some characteristic of the seismic wavefield against time. A seismogram may also be commonly known as a seismic trace. The acquired seismograms may be transmitted wirelessly or over electrical or optical cables to a recorder system. The recorder system may then store, analyze, and/or transmit the seismograms. The seismograms recorded as a result of an activation of a source may be referred to as a shot record or a gather. A plurality of gathers may result from a seismic survey. The seismic data may be used to detect the possible presence of hydrocarbons, changes in the subsurface and the like.
Each seismogram may contain distortions as well as refracted waves. Various techniques have been developed to remove distortions from seismograms. Equipment used in a seismic survey, such as components of the data acquisition system or of the source generation system, may introduce distortions into the seismic data. The seismic data may be corrected to compensate for known, or deterministic, distortions. Such distortions may, for example, be introduced by the actual sensors used to record seismic data. Because the amplitude and phase transfer functions of such systems are known, inverse filters may be constructed to compensate for these distortions.
Surface consistent deconvolution is a well-known technique for processing seismograms to correct for distortions. Surface consistent deconvolution may consist of several steps including the collection of individual amplitude spectra from acquired seismograms, recombination of seismogram spectra from surface consistent spectra for each individual seismogram, computation of inverse filters to whiten the recombined spectra and application of the inverse filters for deconvolution purposes. Surface consistent deconvolution may use information gathered through surface consistent spectral analysis. Surface consistent spectral analysis may be defined as a surface consistent redistribution of amplitude spectra of individual seismograms onto at least global, source, receiver, offset, and common-midpoint terms.
As seismic waves travel through the earth, distortions may occur as some of the energy of the seismic waves is lost due to absorption or dissipative effects, i.e., the energy may be dissipated into heat. A common technique used to correct seismograms to compensate for the absorption effects is absorption compensation filtering, also known as inverse Q-filtering, in which the absorption may first be estimated followed directly by a deconvolution filter to compensate for the found absorption. However, this technique does neither estimate the absorption in a surface consistent way, nor does it preserve the surface consistent wavelet model of the data. Therefore, single trace absorption compensation may not be combined in a meaningful way with processing steps such as surface consistent deconvolution.